drm/exynos: fix wrong pointer access at vm close.

This patch fixes wrong pointer access issue to filp->f_op and
filp->private_data.

The exynos_drm_gem_mmap_ioctl() changes filp->f_op and
filp->private_data temporarily and restore them to use
original ones in exynos_drm_gem_mmap_buffer() but there
was no lock between the changing and the restoring so
wrong pointer access to filp->f_op and filp->private_data
was induced by vm close callback.

So this patch uses mutex lock properly to resolve this issue.

Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
index 4731807..67e17ce 100644 (file)
--- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
@@ -329,17 +329,11 @@ static struct drm_file *exynos_drm_find_drm_file(struct drm_device *drm_dev,
 {
        struct drm_file *file_priv;
 
-       mutex_lock(&drm_dev->struct_mutex);
-
        /* find current process's drm_file from filelist. */
-       list_for_each_entry(file_priv, &drm_dev->filelist, lhead) {
-               if (file_priv->filp == filp) {
-                       mutex_unlock(&drm_dev->struct_mutex);
+       list_for_each_entry(file_priv, &drm_dev->filelist, lhead)
+               if (file_priv->filp == filp)
                        return file_priv;
-               }
-       }
 
-       mutex_unlock(&drm_dev->struct_mutex);
        WARN_ON(1);
 
        return ERR_PTR(-EFAULT);
@@ -400,9 +394,7 @@ static int exynos_drm_gem_mmap_buffer(struct file *filp,
         */
        drm_gem_object_reference(obj);
 
-       mutex_lock(&drm_dev->struct_mutex);
        drm_vm_open_locked(drm_dev, vma);
-       mutex_unlock(&drm_dev->struct_mutex);
 
        return 0;
 }
@@ -432,6 +424,16 @@ int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
        }
 
        /*
+        * We have to use gem object and its fops for specific mmaper,
+        * but vm_mmap() can deliver only filp. So we have to change
+        * filp->f_op and filp->private_data temporarily, then restore
+        * again. So it is important to keep lock until restoration the
+        * settings to prevent others from misuse of filp->f_op or
+        * filp->private_data.
+        */
+       mutex_lock(&dev->struct_mutex);
+
+       /*
         * Set specific mmper's fops. And it will be restored by
         * exynos_drm_gem_mmap_buffer to dev->driver->fops.
         * This is used to call specific mapper temporarily.
@@ -448,13 +450,20 @@ int exynos_drm_gem_mmap_ioctl(struct drm_device *dev, void *data,
        addr = vm_mmap(file_priv->filp, 0, args->size,
                        PROT_READ | PROT_WRITE, MAP_SHARED, 0);
 
-       drm_gem_object_unreference_unlocked(obj);
+       drm_gem_object_unreference(obj);
 
        if (IS_ERR((void *)addr)) {
-               file_priv->filp->private_data = file_priv;
+               /* check filp->f_op, filp->private_data are restored */
+               if (file_priv->filp->f_op == &exynos_drm_gem_fops) {
+                       file_priv->filp->f_op = fops_get(dev->driver->fops);
+                       file_priv->filp->private_data = file_priv;
+               }
+               mutex_unlock(&dev->struct_mutex);
                return PTR_ERR((void *)addr);
        }
 
+       mutex_unlock(&dev->struct_mutex);
+
        args->mapped = addr;
 
        DRM_DEBUG_KMS("mapped = 0x%lx\n", (unsigned long)args->mapped);